Chronic back pain (CBP) is a major health problem in the United States. Neither pure physical models of back pain nor models that focus exclusively on psychological factors seem adequate to explain the functional limitations of CBP patients. The major supposition of this proposal is that appraisals regarding the painfulness of a set of tasks and confidence in ability to perform the tasks will exert a significant impact on actual physical performances beyond that accounted for solely by physiological parameters. In addition, over-predictions of pain will lead to increased activity avoidance. The actual performance on physical tasks will be determined, however, not only by psychological factors but will be constrained by physical limitations as well. Three studies are proposed that are designed to evaluate a comprehensive biobehavioral model of the performance of CBP patients that integrates operant and cognitive variables (i.e., fear of pain and injury, self-efficacy) with physical limitations directly related to injury, physical deconditioning, and maladaptive body mechanics. In this project we will directly test the contributions of each of these variables to performance on ecologically valid, dynamic tasks of physical functioning. Moreover, we postulate that the performance of empirically derived subgroups of CBP patients will be differentially influenced by self- efficacy expectations, fear of activity, and physical perturbations. Specifically, we propose that task-specific psychological factors will have a greater impact on patients who have higher levels of psychological distress, feel less control over their lives and their symptoms, perceive pain to interfere more with their lives, and are less active than those patients who are less psychologically distressed, feel more in control, and who are more active. The primary purpose of this competing continuation is determination of the relative contribution of specific physical and psychological contributors to performance on a set of dynamic functional capacity tasks, and to evaluate the changes in these contributors as a result of an intensive rehabilitation program designed to increase muscle strength, tone, and flexibility, to improve body mechanics; as well as, to reduce fear of activity, to increase the sense of control over pain, and to increase self-efficacy regarding physical capabilities.